Light transmission screen and method of manufacture



June 2%, 1951 J. A. GIBBONS LIGHT TRANSMISSION SCREEN AND METHOD OF MANUFACTURE Filed July 26, 1948 H i w Q INIFNSE MEI-IT ERNIE/0L LIGHT INVENTOR. dflM-S 7. GIBBONS HTTORNEV Patented June 26, 1951 LIGHT TRANSMISSION SCREEN AND METHOD OF MANUFACTURE James A. Gibbons, North Hollywood, Calif., as-

signor to Warner Brothers Pictures, Inc., Burbank, Calif., a corporation of Delaware Application July 26, 1948, Serial No. 40,666

8 Claims. i

This invention relates to screens, and particularly to light intensity reducing screens for balancing the intensity of two light sources.

In the art of motion picture production, many scenes within the camera viewing angle are illuminated by a combination of daylight and artificial light, or parts of the scene are illuminated with daylight and other parts with artificial light. For instance, in the photographing of an indoor scene of a room, the camera angle may include a portion of the interior illuminated by normal artificial light and a window or door through which an outside area is seen by the camera, the outdoor area being illuminated by intense sunlight. Under these conditions, the outside area has a very strong illumination, and it is impractical to illuminate the interior to the same intensity for several reasons, such as the necessity for many lamps, the elimination of detail in the shadows, and inconvenience to the aclors. However, by reducing the light intensity from the outside area, the indoor area may be artificially illuminated in the normal manner, and the film will be properly exposed, and thus, provide a better quality picture.

The present invention, therefore, is directed to a neutral density light reducing screen which reduces the light over all wave lengths of the visible spectrum in equal amounts, so that the exposure of the outside area and interior will have the same definition and proper proportioning in the finished print. Such a screen is one in which dye is applied and absorbed by the screen, the dye absorbing the light, and thus, producing the reduction in light reaching the camera film. The

screen is made of multiple coats of plastic material, is light, tough, and, when mounted in is frame, may be easily moved about to the desired locations.

The principal object of the invention, therefore, is to facilitate the obtaining of light intensity balances between areas having different illuminations.

Another object of the invention is to provide an improved light reducing screen for large areas.

A further object of the invent-ion is to provide an improved plastic light filter for balancing the light intensity between various areas having different illuminations.

A still further object of the invention is to provide an improved method of constructing a multiple layer plastic screen having uniform light reducing properties throughout.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the appended claims, the manner of its organization and the mode of its operation will be better understood by referring to the following description read in conjunction with the accompanying drawings, forming a part hereof, in which:

Fig. 1 is a diagrammatic view showing one use of the invention.

Fig. 2 is an elevational view of the screen mounted in its frame, and

Fig. 3 is an enlarged cross-sectional view illustrating the construction of the screen.

Referring now to the drawings, a camera 5 is set up within an interior 6, the camera viewing angle being within the dot-and-dash lines 1. The scene within the angle may constitute the walls l0 and ll of a room, counters or tables l2 and I3, and actors I6 and Il, the actor l6 walking from the position ill to the position l6 during the sequence. The room has a door 20 and a window 2|, the camera, of course, photographing viewable objects through the door and window, such as a building 24 and side walks 25 and; 26, the side walks being on the sides of a street 21. In photographing such a scene, it is obvious that the camera will not only see the interior, but also the exterior through door 20 and window 2 I, and that the exterior may be illuminated by intense daylight, while the interior is illuminated b artificial light. If suflicient artificial light were supplied to the interior to balance the intense daylight of the exterior, the interior light would be so intense as to be impractical for the reasons mentioned above. Thus, to permit the use of normal artificial light, the street light is reduced by, the positioning of a screen 30 in'front of the door and window, which screen is made in accordance with the invention.

Referring now to Fig. 2, the screen 30 is mounted in the usual manner within a rigid frame 3| and laced by rubber bands or cords 32 through gromets in the screen and holes in the frame.

Referring now to Fig. 3, the screen is shown for purposes of illuslration as made up of a plurality of coats or layers 34, in which the two last layers onthe right are shown impregnated by a dye. Although the dye is shown in onl these layers, it is to be understood that it may extend to only one layer or into more than two layers in accordance with the amount of light reduction required. Furthermore, since each layer or coat is of the same material, there is actually no line of separation between layers, the screen being homogeneous.

Referring now to the actual construction of application,

Toluene The screen is made of a formula which I refer to as M-3, and given hereinafter, the dye being applied after the required number of coats have been applied to build the screen up to the desired thickness. For instance, the base solution is first placed in a dip-pan and the surface of a matrix on a cylindrical drum is passed therethrough to apply each coat, which is dried before the application of the next coat. The base is generally of suflicient tensile strength and toughness after the application of six coats, which provides a screen of substantially .007 inch thick. The formula for the base layers is as follows:

Ethyl cellulose gms 744 Xylol cc 3468 Ethylene glycol monomethyl ether cc 827 Butyl alcohol cc 82'7 Methyl isobutyl ketone cc 827 Methyl phthalyl ethyl glycollate cc 48 The above formula is adjusted to a viscosity of 42 at 24 degrees C., the application speed for a drum of approximately five feet, ten inches in diameter, being one revolution in sixteen minutes.

The formula for the dye coat solvents is as follows:

Cc. Benzyl alcohol 150 Butyl alcohol 450 Methyl Cellosolve 300 Ethylene dichloride 225 Pent-acetate '75 Ethanol 1125 Butyl Cellosolve 675 while the dye formula is as follows:

Grams Methyl red (C concentrated) 6.444 Methyl blue (MB concentrated) 10. Methyl yellow (G concentrated) 12.333

The solvents and dyes are thoroughly mixed and placed in a dip-pan and applied by revolving the drum, and thus, rotating the homogeneous base. The base is allowed to dry for at least two hours before applying the dye coat.

The above screen has a neutral density that decreases the intensity of all components of the visible spectrum in substantially the same proportion, and by varying the dye coat, will produce different amounts of light reduction, the above formula being that used for bright sunlight to balance normal artificial light in an interior such as illustrated in Fig. 1. That is, the above dye formula provides sixty-five percent absorption of light, only one dye coat being applied at a drum speed of one revolution in ten minutes,

the drum having a diameter of approximately five feet, ten inches. To vary the absorption, the drum speed is varied. For instance, to determine the drum speed for a specific value of light absorption, a drum having an approximate circumference of fifteen feet has its speed varied each three feet, thus providing five test strips. This permits a graph of drum speed versus light transmission to be made, the drum being rotated at a constant selected speed for the final screen, the dye being uniformly applied to the entire screen.

If the desired absorption is not within the range of speeds selected for proper application of the dye coat, the dye formula may be strengthened or weakened by proportionately increasing the dye ingredients with respect to the solvents and another series of speed tests made. 1 By comparing the strips with established filters of known absorptions, using the log sector for photo-spectrometer tests, the desired speed of rotation for the drum is determined.

The screen is cut by strings placed under the last coat of the base and then stripped from its matrix and placed in the frame 3i of proper size. It is then ready for use as described above.

I claim:

1. A light filter screen comprising a base made up of a plurality of layers, each layer being formed from ethyl cellulose, xylol, ethylene glycol monomethyl ether, butyl alcohol, methyl isobutyl ketone, and methyl phthalyl ethyl glycollate, certain of said layers having absorbed therein a mixture of substantially twenty-two percent red, substantially thirty-five percent blue, and substantially forty-three percent yellow dyes to provide a neutral density screen having a predetermined value of light absorption depending upon the amount of said mixture absorbed therein, said screen decreasing all visible color components substantially in the same proportion.

2. A light filter screen in accordance with claim 1, in which ,said dye mixture proportions are substantially 18.444 gms. of methyl red, 10 gms. of methyl blue, and 12.333 gms. of methyl yellow.

3. A light filter screen in accordance with claim 1, in which substantially 6.444 gms. of methyl red, 10 gms. of methyl blue, and 12.333 gms. of methyl yellow are dissolved in the following solvents having substantially the following proportions:

Cc. Benzyl alcohol 150 Butyl alcohol 450 'Methyl Cellosolve 300 Ethylene dichloride 225 Pent-acetate Ethanol 1125 Butyl Cellosolve 675 4. A light filter screen in accordance with claim 1, in which the ingredients of said base layers have substantially the following proportions:

and said dye mixture has the following ingredients of substantially the following proportions:

Solvents- Benzyl alcohol cc 150 Butyl alcohol cc 450 Methyl Cellosolve cc 300 Ethylene dichloride cc 225 Pent-acetate cc 75 Ethanol n cc 1125 Butyl Cellosolve cc 675 Dye- Methyl red (concentrated) gms 6.444 Methyl blue (concentrated) 'gms 10. Methyl yellow (concentrated) gms. 12.333

5. The method of constructing a neutral density light absorbing homogeneous screen comprising forming a base by passing a dry surface of a matrix having a surface layer composed of cellulose acetate, acetone, ethanol, propane, ethylene glycol monomethyl ether acetate, and toluene through a, base solution of ethyl cellulose, xylol, ethylene'glycol monomethyl ether, butyl alcohol, methyl isobutyl ketone, and methyl phthalyl ethyl gly'collate, applying additional .Ieet per minute.

7. A filter screen for decreasing all visible color components in substantially the same proportions, comprising a plurality of separately applied layers of a cellulose base, said base being homogeneous and containing a mixture of substantially 6.5 gms. of methyl red dye, 10 gms. of methyl blue dye, and 12.3 gms. of methyl yellow dye dissolved in a solvent, the amount of said mixture in said base controlling the amount of light absorption by said screen.

8. The method of producing a filter screen for decreasing-all visible color components in substantially equal proportions, comprising successively applying a plurality of liquid layers of a cellulose base to obtain a screen thickness of approximately .007 inch, drying each layer before the application of the next layer, and applying to the last layer a dye solution containing a mixture of substantially 6.5 gms. of methyl red dye, 10 gms. of methyl blue dye, and 12.3 gms. of methylyellow dye in an amount determined by the light absorption required.

JAMES A. GIBBONS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS I Number Name, Date 1,776,269 Pomeroy Sept. 23, 1930 1,841,274 Ballard Jan. 12, 1932 2,072,858 Ellis Mar. 9, 1937 2,257,999 Bodde Oct..7, 1941 2,315,974 Malm et al. .Apr. 6, 1943 2,370,263 Schweizer Feb. 27, 1945 2,418,605 Shepherd et al. Apr. 8, 1947 2,444,492

Blout et a1. July 6, 1948 

